The present invention relates to brakes, and more particularly to a brake apparatus that provides a remote indication of the need to replace friction pads.
Brakes of the type used on automobiles, aircraft and other vehicles employ high friction brake pads attached by rivets to shoes which are connected to the vehicle frame so they cannot rotate. When the brake is applied, the shoe is moved to engage a smooth metal member in the form of a disk or drum that rotates with a wheel of the vehicle. Friction between the stationary pad and the rotating member provides the braking force. The friction surface of the pad is gradually worn away until the pad has been consumed and must be replaced.
If expensive repairs are to be avoided, it is imperative that the pads be replaced before they are worn to the point at which the rivets contact and score the rotatable member. The life expectancy of a pad may be predicted, within broad limits, based on the wear resistance of the material of which it is made and the working thickness between its original friction surface and the heads of the rivets. Nevertheless, variations in individual driving habits make accurate prediction of replacement intervals impossible. Most vehicles, therefore, require frequent visual inspection of brake pads, which is a time-consuming and inconvenient process, to guard against brake damage. Failure to inspect brake pads with sufficient frequency is not unusual.
It is therefore highly desirable to provide an indication on the instrument panel of the vehicle of the need to replace brake pads, thus eliminating the need for pad inspections. Various arrangements have been proposed to this end, one of which is described in U.S. Pat. No. 3,869,695, to Kita. It utilizes an electrical wire embodied in the pad and protruding above the level of the rivets so that it is severed by the action of a disk or rotor before the rotor contacts the rivets. An electronic circuit is responsive to the severance of this wire to produce an indication that the pad should be replaced. Unfortunately, the circuit is relatively complex and must remain active whenever the vehicle is in use to sense the severance. Rotor action is sensed only at the point where the wire is located and misalignment of the brake shoe may cause earlier contact with rivets at another portion of the pad, permitting the rotor to be damaged before any warning is given. Another disadvantage of the previously known system is that it requires a considerable quantity of copper wire, which is both expensive and heavy, connecting each wheel to the instrument panel.
An objective of the present invention is to provide an improved, relatively inexpensive and greatly simplified pad-wear indicator. Another objective is to provide such an indicator that reliably senses the need for pad replacement at the proper time regardless of any misalignment between the pad and the rotating brake member by which it is engaged.